Alain Chauvin

Transmission of Bartonella henselae by Ixodes ricinus

The causative agent of cat-scratch disease in humans can be transmitted by this tick through saliva.

Babesia and its hosts: adaptation to long-lasting interactions as a way to achieve efficient transmission.

Babesia, the causal agent of babesiosis, are tick-borne apicomplexan protozoa. True babesiae (Babesia genus sensu stricto) are biologically characterized by direct development in erythrocytes and by transovarial transmission in the tick. A large number of true Babesia species have been described in various vertebrate and tick hosts. This review presents the genus then discusses specific adaptations of Babesia spp. to their hosts to achieve efficient transmission. The main adaptations lead to long-lasting interactions which result in the induction of two reservoirs: in the vertebrate host during low long-term parasitemia and throughout the life cycle of the tick host as a result of transovarial and transstadial transmission. The molecular bases of these adaptations in vertebrate hosts are partially known but few of the tick-host interaction mechanisms have been elucidated.

Immunity against helminths: interactions with the host and the intercurrent infections.

Helminth parasites are of considerable medical and economic importance. Studies of the immune response against helminths are of great interest in understanding interactions between the host immune system and parasites. Effector immune mechanisms against tissue-dwelling helminths and helminths localized in the lumen of organs, and their regulation, are reviewed. Helminth infections are characterized by an association of Th2-like and Treg responses. Worms are able to persist in the host and are mainly responsible for chronic infection despite a strong immune response developed by the parasitized host. Two types of protection against the parasite, namely, premune and partial immunities, have been described. Immune responses against helminths can also participate in pathogenesis. Th2/Treg-like immunomodulation allows the survival of both host and parasite by controlling immunopathologic disorders and parasite persistence. Consequences of the modified Th2-like responses on co-infection, vaccination, and inflammatory diseases are discussed.

Humoral and cellular immune responses to Fasciola hepatica experimental primary and secondary infection in sheep

Blood leukocyte changes, serum hepatic enzyme levels, lymphocyte proliferation in response to Concanavalin A (ConA) and to parasitic excretory-secretory products (FhESP), and antibody (IgG and IgM) responses (ELISA and Western blot) were studied in sheep, the natural susceptible host of F. hepatica, during the first 3 months of an experimental primary or secondary infection. The proportion of flukes established was similar in once- and twice-infected groups, but the flukes originating from the secondary infection migrated more rapidly to the bile ducts. Primary infection induced a marked peripheral eosinophilia from 3 to 13 weeks post-primary infection (PPIW). FhESP-specific IgM were produced from PPIW 2 with peaks in PPIW 3 and 9-10; FhESP-specific IgG increased from PPIW 2 to 6 and became stable afterwards. Western blotting revealed 12 major antigenic fractions in FhESP from 12, 15, 20, 24, 27, 28.5, 30, 41, 51, 56, 69 and 156 kDa; some non-specific ones have been characterized. A sequential recognition of higher then lower molecular weight antigens was observed. FhESP-specific lymphocyte proliferation was marked from PPIW 2 to 5. In contrast, ConA stimulation of lymphocytes was decreased. After secondary infection in PPIW 6, immune responses were modified. The ConA-induced lymphocyte proliferation was transitorily increased. In contrast, the humoral response, in particular against the early recognized antigens, and the level and the duration of the FhESP-specific lymphocyte proliferative response, were reduced.

Babesia sp. EU1 from Roe Deer and Transmission within Ixodes ricinus

We report in vitro culture of zoonotic Babesia sp. EU1 from blood samples of roe deer in France. This study provides evidence of transovarial and transstadial transmission of the parasite within Ixodes ricinus, which suggests that this tick could be a vector and reservoir of EU1.

Transstadial and transovarial persistence of Babesia divergens DNA in Ixodes ricinus ticks fed on infected blood in a new skin-feeding technique.

Although Babesia divergens is the the principal confirmed zoonotic Babesia sp. in Europe, there are gaps in our knowledge of its biology and transmission by the tick Ixodes ricinus. In order to reproduce the part of the parasite cycle that occurs in the vector, an in vitro animal skin feeding technique on blood containing in vitro cultivated B. divergens was developed. Parasite DNA was detected in all samples of salivary glands of nymphs and adults that had fed on parasitized blood as larvae and nymphs, respectively, indicating acquisition as well as a transtadial persistence of B. divergens. PCR performed on eggs and larvae produced by females that had fed on parasitized blood demonstrated the existence of a transovarial transmission of the parasite. Gorging B. divergens infected larvae on non-infected gerbils showed persistance of the parasite over moulting into the resulting nymphs. These results indicate that the parasitic stages infective for the vector (i.e. the sexual stages) can be produced in vitro. To our knowledge, this is the first report of artificial feeding of I. ricinus via membrane as well as in vitro transmission of B. divergens to its vector. The opportunities offered by the use of such a transmission model of a pathogen by I. ricinus are discussed.

Babesiosis in Immunocompetent Patients, Europe

We report 2 cases of babesiosis in immunocompetent patients in France. A severe influenza-like disease developed in both patients 2 weeks after they had been bitten by ticks. Diagnosis was obtained from blood smears, and Babesia divergens was identified by PCR in 1 case. Babesiosis in Europe occurs in healthy patients, not only in splenectomized patients.

Natural Transmission of Zoonotic Babesia spp. by Ixodes ricinus Ticks

To determine characteristics of natural transmission of Babesia sp. EU1 and B. divergens by adult Ixodes ricinus ticks, we examined tick salivary gland contents. We found that I. ricinus is a competent vector for EU1 and that their sporozoites directly invade erythrocytes. We conclude that EU1 is naturally transmitted by I. ricinus.

Lack of genetic structure among Eurasian populations of the tick Ixodes ricinus contrasts with marked divergence from north-African populations☆

Host-parasite interactions may select for significant novel mutations with major evolutionary consequences for both partners. In poor active dispersers such as ticks, their population structures are shaped by their host movements. Here, we use population genetics and phylogeography to investigate the evolutionary history of the most common tick in Europe, Ixodes ricinus, a vector of pathogenic agents causing diseases in humans and animals. Two mitochondrial and four nuclear genes were sequenced for 60 individuals collected on four geographical scales (local, regional, Eurasian and western Palearctic scales). The overall level of nucleotide diversity was low and the variability did not differ at the local, regional or Eurasian scales but increased two fold for the western Palearctic scale. Moreover, the phylogenetic trees indicated an absence of genetic structure among Eurasian ticks, contrasting with a strong differentiation of the north-African ticks which formed a divergent clade. The homogeneity in Eurasian ticks may be explained by gene flows due to passive dispersal of ticks by hosts within a continuous population and recent range expansion of I. ricinus as shown by the fit of the observed frequency distribution of numbers of mismatches between pairwise sequences with the demographic expansion model (Harpending raggedness index, P=0.74). The genetic divergence of the north-African populations could be explained by genetic drift in these small populations that are geographically isolated and/or selection pressures due to different ecological conditions (seasonal activity, pathogenic agents and hosts communities). The consequences of these results on the epidemiology of vector-borne diseases are discussed.

A new ovine Babesia species transmitted by Hyalomma anatolicum anatolicum

The pathogenicity and morphology of a large Babesia species, Babesia sp. Xinjiang, are described here. The parasite has very low virulence for sheep, and caused no detectable clinical symptoms. Splenectomized sheep infected with the parasite showed mild fever and low parasitemia and would recover gradually. If splenectomized sheep were immuno-suppressed with dexamethasone, the parasitemia could reach 8.5%, and death occurred. A splenectomized calf could not be infected with the Babesia species. Paired parasites were the typical form of the Babesia species in erythrocytes and the average size of a pair of parasites was 2.42 (+/-0.35) microm x 1.06 (+/-0.22) microm. Merozoites were found in the gut, salivary gland, haemolymph, ovary and eggs of female Hyalomma anatolicum anatolicum engorged on sheep infected with the parasites. The results of experimental transmission showed that the larval, nymph and adult stages of H. a. anatolicum could transmit the Babesia species to sheep.